Yamaha YZ125

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Engine124 cc single-cylinder, water-cooled, two-stroke, case reed
Power33 hp[1]
Torque19 ft·lbf[2]
SuspensionMonoshock, 13 inches travel
Brakesdouble disc
Tires80/100-21, 100/90-19
Wheelbase57.8 inches
Seat height38.7 inches
Weight189 lb (dry), 196 (wet)
Fuel capacity2.1 gallons
RelatedYamaha YZ250F

The Yamaha YZ125 is a 125 cc two-stroke motorcycle designed for motocross riding. The motorcycle is made by Yamaha and is one of their flagship bikes. It was first produced in 1974 (originally titled "YZ125 Monocross") and has continued production with a new model being produced every year to date. The YZ 125's produced from 1996-2000 are considered by some to be the best dirt bikes ever, due to its wide powerband and excellent handling. [3] The YZ 125 has been ridden to 5 AMA National Motocross Championships, and multiple AMA Regional Supercross Championships [4]

In 2001, Yamaha released a bike designed to compete with the YZ125, the four stroke YZ250F. The two bikes share a rolling chassis and are eligible to compete in the same racing class.


The YZ 125 has had a liquid-cooled 124 cc, case-reed, 2 stroke engine since 1981, from 1974-1980 models had air-cooled and had a 32mm Mikuni. It breathes through a 38 mm TMX carburetor made by Mikuni. Stock, the engine produces 33 horsepower at the rear wheel. The YZ125 is capable of reaching speeds of 71 miles per hour stock. [1]


The YZ125 has been built with 5 and 6 speed gearboxes depending on model year (one down, five up) or (one down, four up) sequential gearbox. The 2007 model has a Constant mesh wet, multiple-disc coil spring clutch. The revised gear ratios as of the 2007 model are:

  • Gear Ratio - 1st Gear 31/13 (2.385)
  • Gear Ratio - 2nd Gear 29/15 (1.933)
  • Gear Ratio - 3rd Gear 27/17 (1.588)
  • Gear Ratio - 4th Gear 23/17 (1.353)
  • Gear Ratio - 5th Gear 24/20 (1.200)
  • Gear Ratio - 6th Gear 23/21 (1.095)


From 1974 through 2004, the YZ 125 had a single backbone frame made from steel. It generally averaged between 176 and 198 pounds. For the 2005 year, however, Yamaha switched to a twin spar frame constructed from an aluminum alloy. This frame material change dropped the weight to 190 lb.(dry weight) For 2008 models, additional weight savings in the wheel assemblies and front fork suspension have yielded additional weight savings making wet weight, no gas sub-200 lbs. Aluminum framed YZ125's are notably 'flickable' and sometimes this trait is seen as a drawback since they tend to become more difficult to control on rough surfaces. [5]

Electrics & Wiring

As the YZ125 is a motocross bike designed for speed and racing, there is no battery, electric start, or headlight. The YZ125 has CDI ignition (Capacitor discharge ignition) with a rev limiter set at the 13,000 rpm redline. [1]

External links